1. Field of the Invention
The present invention relates generally to identification means having diffraction gratings disposed thereon provided for security and authentication and, more particularly, but not by way of limitation, to novel method and apparatus for determining if such a diffraction grating has been forged.
2. Background Art
In the parents of the present application, and particularly in Ser. No. 07/921,460, there is described method and apparatus for reading a compound diffraction grating and an associated magnetic strip. Such optical images and magnetic strips are provided on identification means, such as credit cards, to assist in authentication of the identification means and to prevent or deter forgery of such identification means.
Some diffraction gratings which may be employed comprise a plurality of different individual gratings of varying widths. Such compound diffraction gratings are expensive to copy and, since credit cards, for example, typically have low maximum charge limits, it is uneconomical to incur the expense of copying one. It is also expensive to build a forged compound diffraction grating from individual diffraction grating elements, since it is extremely difficult to insert grating elements of the necessary precise widths.
The possibility exists, however, that a forger might create a master grating having closely spaced grating elements of the type used in the compound diffraction grating. The forger would then create individual sections of the compound diffraction grating by obliterating all but the type of diffraction grating element desired for each particular section. The obliteration could be by laser and the process could be automated and relatively inexpensive.
Accordingly, it is a principal object of the present invention to provide method and apparatus for detecting when diffraction gratings on identification means have been forged.
It is a further object of the invention to provide such method and apparatus that are easily and economically employed and may be employed while the identification means is being authenticated.
Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures.